1. Field of the Invention
The present invention relates generally to a dielectric ceramic composition, which is a glass-ceramic composite material for low temperature firing, and more particularly, to a dielectric composition for use in a microwave resonator, a LC filter, a laminated capacitor, and a multilayered circuit board or the like.
2. Description of the Related Art
With miniaturizing of the electronic devices such as microwave resonators and microwave filters, efforts have been made to replace cavity resonators with ceramic dielectrics having a high relative dielectric constant. Resonators and the filters are miniaturized by use of an effect that a wavelength of electromagnetic waves in dielectrics is shortened to 1/.epsilon.r.sup.1/2 times that in free space, wherein .epsilon.r represents the relative dielectric constant of dielectrics.
However, the dielectric material has not met the recent demand for further miniaturization since the relative dielectric constant .epsilon.r of a ceramic dielectric material having a temperature coefficient suitable for use as a dielectric resonator has so far been limited to 100 or less.
A method employing an LC resonator, which has conventionally been known in microwave circuits, is effective for meeting the demand under restriction of a relative dielectric constant .epsilon.r of a ceramic dielectric material. Thus, a further miniaturized electronic apparatus having high reliability may be produced by applying to fabrication of LC circuits a lamination method which is adapted in practice for a laminated capacitor and a multilayered board.
However, producing an LC resonator having a high Q value in a microwave region by way of a lamination method requires high electric conductivity of an internal electrode which is built into the laminated capacitor and the multilayered circuit board. A metal having high electric conductivity such as gold, silver or copper must be used for the internal electrode which is fired simultaneously with a dielectric or a multilayered circuit board. For this reason, a dielectric material must be able to be sintered at low temperature simultaneously with internal electrodes formed of a metal material having a low melting point, and as well must have a high dielectric constant, a high Q value and enhanced temperature stability. However, a dielectric material which meets all of these criteria has not yet been found.